Method and apparatus for grinding or polishing metal sheets



Oct. 17, 1944. T. J. MASSE 2,360,504

METHOD AND APPARATUS FOR GRINDING OR POLISHING METAL SHEETS Filed July28, 1959 5 Sheets-Sheet l Fig.5

LNV E N T 0 RV THOMAS JEROME MA 575E SATTOTZNEYS Oct. 17, 1944. J, ss2,360,504

METHOD AND APPARATUS FOR GRINDING OR POLISHING METAL SHEETS Filed July28, 1959 s Sheets-Sheet 2 l NVE NTO R THOMAS JEROME MA SSE ATTORNEYS 3Sheets Sheet 3 E m M 5 R M k H w 4 m m N x 9 w m m E R 6 a 6 V O 2 .M 37. 8 i! 7 N M W 5 5 6 5 8 4 7 l 5 w 6 v w 7 o 7 L o m A a N 5 w r N w III I III l I ||l.| I 7/ A z 1/ 1 \M\ .7//////lln\\ B 1| If} Hun F.HHHHHHHHHH MHHHHH I MHHHH HHMM A .m 0 u 2 6 O i 6 v G L 00 8 5 7 w 6 H w6 w 6 8 METHOD AND APPARATUS FOR GRINDING 0R POLISHING METAL SHEETS I "fFiled Jilly 2a, 1959 roll.

Patented Oct. 17; 1944 UNITED STATES PATENT OFFICE METHOD AND APPARATUSFOR GRINDING OR POLISHING,METAL SHEETS .Thoinas Jerome Masse,Alexandria, near Sydney, New South Wales, Australia, assignor to TheEdes Manufacturing Company, 7 Plymouth, 7

Mass, a corporation of Massachusetts Application July 28, 1939, SerialNo. 286,953

In Australia March 29, 1939 23 Claims.

This invention relates to a new method and apparatus for grinding orpolishing the surfaces of metal sheets.

In the usual method of grinding sheets of zinc,- copper, and other hardmetals to produce thereon a smooth surface, as in the manufacture ofphotoengraving plates, the grinding is effected by'trav-' ersing eachsheet repeatedly under a felt roll which rotates on'a horizontal axisand distributing an abrasive powder onto the surface of the sheet as itpasses under the roll.

In the practice of this usual method it is impossible continually toproduce sheets with a uniform smooth surface finish. The rotary pad soonbecomes more worn at some places along its length than at others, sothat the pressure and I grinding action of the pad on the sheet is notnomi'cal recovery of metal values which are removed from the surface ofthe sheets during the grinding operations. The metal particles are sointermingled with the grinding powder that the trouble and expense ofeffecting a separation are not warranted.

The present invention has been'devised with the object of avoiding thesedefects which are incident to the known sheet surface grinding methodsand machines, and this invention provides a new method and apparatus bywhich the grinding and polishing of metal sheets may be carried out moreuniformly and more efficiently than heretofore; and with the production;of ground and polished sheets of improved quality.

According to the method of the present invention, the surface of themetal sheet or sheets to be ground is subjected uniformly to thegrinding or polishing action of a small abrasive-surfaced pad or padswhich rotate at high speeds in circular'swaths or whorls on thesheetsurface, about an axis substantially vertical to the sheet. The

- abrasive is fixed to the pad, so that there is subit is impossible toensure uniform distribution of the powder over the sheet surface, andthis introduces further irregularities and non-uniformities in thesurface finish.

Moreover, as metal particles are ground from the surface of the sheet,some of the metal sticks in the pad face and clogs it or is overtaken bythe pad in its continued rotation and caught under it. The clogging ofthe pan with metal results in metal-to-metal contact; when this occursthe metal seizes, and scratches are produced on the surface of thesheet. In the use of the conventional grinding method, therefore, thepad soon becomes inefficient, losing its optimum grinding or polishingaction and producing scratches on the surface of the sheet. Whendetectable scratches appear the grinding must be prolonged until thescratches have been worked out. The grinding sometimes must be carriedon for so long a time that the sheet is diminished in thickness and isthereby rendered unsatisfactory for use by photo-engravers or by otherartisans in whose work sheets of great accuracy in thickness andsubstantially perfect in surface finish are required.

A further objectionable feature of the usual grinding method is thatthere can be no ecostantially no free abrasive on the sheet. During thegrinding of the sheet by the revolving pad the sheet is moved to and froin a linear path beneath the pad, and at the same time the revolving padis moved bodily to and froover the sheet in a. cross-wise linear path.These movements are controlled so as to ensure uniform coverage of theentire sheet by the abrading means. The pressure of the revolving pad onthe sheet surface is kept constant by mounting the same for movement invertical direction and applying a constant pressure to the same duringsuch manner as to pick up and flush aw'ay'partia cles of metalimmediately after they have been removed from the sheet by the abrasiveheld on the pads. The application of the flushing liquid has the furtherimportant function of maintaining a protective liquid film'between-theabrasive and the sheet surface, which allows theiabrasive to actupon themetal to the desired extent but keeps it from digging freely into themetal or producing comparatively deep scratches" which might interferewith the useof the finished sheets in photo-engraving work. Thiscontinuousfiushing of the free metal particles away from the grindingzone essentially involves an operation in which the flushing'liquid isflooded onto the sheet, from a point inside the circular path or orbitof the grinding pad or pads, so as to flow path of movement of the pads.The surface of the sheet where the grinding is being carried out is keptclean and free of metal particles to such an extent that the pads do notpick up metal particles and become clogged but, instead, continue togive uniform and highly satisfactory grinding or polishing effects overlong periods of use.

The particles of metal ground from the sheet are carried away from thesheet in the flushing liquid, and the liquid is then filtered orotherwise clarified to separate and recover the metal, which may bereused or disposed of as desired to effect an important saving over theusual practice. The clarified flushing liquid may be recirculated andreused in the same cycle of operation.

The flushing medium employed in this method may be kerosene, stearineoil or any other suitably mobile non-corrosive liquid which allows theabrasive to perform its function without damaging the sheet surface andat the same time picks up and removes the particles of free metalabraded from the sheet. Kerosene is the preferred flushing liquid in thegrinding or polishing of zinc sheets, while stearine oil is preferred inthe case of copper sheets.

The apparatus of the present invention is an eflicient and practicalapparatus for carrying out the grinding or polishing of metal sheetsaccording to the above-mentioned method. In general, the apparatusincludes a horizontal movable work table upon which the sheets are heldduring the grinding operation, one or more vertical spindles, eachhaving a rotary grinding head at its lower end on which anabrasive-surfaced grinding pad or pads are fastened, means for revolvingthe spindles at high speed, means for traversing the work table to andfro beneath the revolving pads in a rectilinear path, and means fortraversing the revolving spindles and pads to and fro across the worktable in a rectilinear path at an angle to the path of the table. Eachspindle is mounted for revolution at high speed about a vertical axis,and means are provided for holding the abrading means against thesurface of the sheet under constant pressure while permitting variationsin the vertical position of the spindle and the horizontal plane of thegrinding pad during the grinding operation. The apparatus also comprisesmeans for continuously supplying a stream of flushing liquid onto thesurface of the metal sheet at a point disposed inside the grinding pathor orbit of each grinding pad, such means preferably including a hollow.spindle for the grinding head, an openin'g allowing passage of liquidfrom the spindle onto an underlying sheet, and means for feeding theliquid into and through the spindle during rotation thereof at highspeed.

iThe spindles are provided with means for effe'ctingpositive movementthereof in a vertical direction, while either revolving or notrevolving, in order to raise the grinding pads off the surface of asheet or sheets on the work table.

of the table I0.

The machine is constructed so that the spindles may be driven at highspeeds; e. g. by belts, without imposing transverse strains thereon andwithout restricting the ability to move the spindles and pads invertical direction while they are being driven.

A pair of abrasive pads preferably are mounted in spaced relation oneach rotary grinding head of the apparatus, there being an open spacebetween the pads to allow for the flooding of the flushing liquid ontothe sheet from the outlet of the revolving spindle.

An illustrative embodiment of apparatus for use in accordance with myinvention is shown in the accompanying drawings and described more fullyhereinbelow. In the drawings,

Figure l is a longitudinal sectional elevation of the apparatus.

Figure 2 is a transverse sectional elevation.

Figure 3 is a side elevational view of one of the grinding spindle, headand pad assemblies.

Figure 4 is a vertical section through the assembly of Figure 3, and

Figure 5 is a plan of the chain and sprocket arrangement for driving thetable.

Figure 6 is a horizontal section along the line 66 of Figure 4.

Referring to the drawings for illustrative details, the machine table Inis traversible lengthwise on a pair of horizontal rails H which arefixed to the machine bed 12.. Flanged runner wheels l3 are secured tothe under side of the table to run on the rails II. A gutter I4 is fixedaround the sides and ends of the table to collect liquid flowing off thetable.

Traverse motion is applied to the table through a pair of continuouschain belts [5 which are carried over end sprocket wheels l6 and H whichare driven by the motor 2| through gears 23, a

chain belt 22, sprockets 24 and chains 25 (see Figures 2 and 5).straddled between and secured to chains I5 is a spindle l8 which carriesa slide block l9. Block I9 is fitted to slide in a driver fork 20 whichis fixed to the under side The slide block I9 is carried along with thechain belts l5. Working in the fork 20, it applies longitudinal to andfro movement to the table along the rails II at a slow rate.

As shown in the drawings, the slide block [8 is fitted closely in thedriving fork 20. In practice, a clearance of an inch, more or less, maybe provided between the block and the fork, in order I to cause a pausein the longitudinal movement of the table at each end of its stroke.Such a pause may be desired to ensure that the degree of grinding in theimmediate vicinity of the ends of the sheets will be the same as thedegree of grinding on the intermediate area of the sheet. It isimportant that the reversing of the table movement shall be gradual andnot rapid, and this slowing down and slow restarting of the tablesmovement is provided for in the illustrated embodiment by the continuouschain drive transmitted through the block or pin carried by the chains,since the longitudinal component of the movement of the block or pin I9,when making its circuit around the sprockets l6 and I1, diminishesgradually to zero and increases gradually from zero.

Rails 30 on a transverse bridge 3| above the table I0 carry a carriage32 on which two grinder spindles and associated mechanisms 33 and 34 aremounted. To and fro traverse movement is applied to the carriage 32through a pair of chain belts 35 and a slide block 36 working in a fork31. The chains 35 run over and between sprockets 39 and 40.

For the same reason as described in reference to the longitudinalmovement of the table I0, it is important that the movement of thecarriage 32 with respect to the table shall be slowed up gradually andre-started gradually. The weight of the carriage is considerable and itsrate of slide movement is relatively rapid, so that the importance ofobviating rapid reversals of its movements is accentuated. If thereversals were rapid, vibration would .be caused and mechanical injurywould result. For these reasons the carriage 32 is driven by thecontinuous chain arrangement 35, or by some other equivalentarrangement. In that form of drive, the longitudinal component of themovement of the block 36 in passing around the sprockets 39 and 40gradually slows up to zero and gradually re-starts from zero in theopposite direction. The traverse-movements of the carriage 32 aretherefore gradually commenced and gradually terminated at zero and aretherefore quite smooth. One pair of the end sprockets over which thechain belts 35 run is driven by an electric motor 44 through a reducingpulley 43 and chain belts 4 I.

As shown in Figure 1, a drain tube 46 depends from the gutter I4 andserves to drain liquid and powdered metal into a sump tray 41. From thetray 41 this mixture of metal powder and liquid passes to a clarifierchamber 48, in which the liquid is separated from the metal. Theclarified liquid runs from ,the chamber 48 into a pump suction chamber49, whence it is pumped for recirculation to the spindles lby operationof a pump 45. The same liquid (subject to replenish-, merit) may be usedrepeatedly on the table. Pump 45 is driven by motor 44.

As seen in Figures 1 and 2, the mechanisms 33 and 34 include verticaltransmission shafts I which are driven by an electric motor 58. Thetransmission shafts 5| for the spindles are both belted to. the motor50, and they run in ball bearing 52 and 53 which are mounted on fixedyokes 54. (Figures 3 and 4.) Driving pulleys for the shafts 5| are shownat 55. Both shafts 5| are hollow. The bottom end 56 of each shaft 5I istelescopically connected to the top end of a hollow spindle 51, and isfitted with fork arms 58 which carry leaf springs I69 in spaced relationto their lower extremities. Springs I39 coact with cross trees 68 whichextend laterally from a head piece 59 fixed on the top end of thespindle 51. Leaf springs I69 bear against the trees 68 and drive thespindle 51. Fork arms 58a. act as stops for the cross trees 68.

It will be understood that this construction and arrangement of thedriving means and spindle permit the spindle 51 to be moved verticallywith respect to the lower end portion 56 of shaft 5I while the spindle51 is either revolving or at rest, and also that the spindle 51 is freefrom constraint by the driving belt.

bearings 66 and 61. The carrier 69 is splined for vertical movement inthe bore 65a. It is pressed downward by a. pair of adjustable helicalsprings 18 in tension. The lower ends of those springs 10 are hookedonto cross arms H which .project laterally from the member 65, and theirtop ends are hooked onto cross arms 12 which project laterally from ahead piece 13 which is screwed onto the top end of the carrier 69. Aflexible dust collar 14, of leather or fabric, is clamped by rings 15 tothe head piece 13 and the casing member 65. A similar flexible collar 16connects the bottom end of the casing member 65 with a foot collar 11 onthe carrier 69. The tubular socket 83 of the grinding head 80 is screwedonto the bottom end of the hollow spindle 51, which projects downthrough the foot collar 11.

Th grinding head 80 comprises a cross head bar 8I secured by screws 82to a flange portion of the socket 83. A spring clip 84 is fixed to eachside of the bar 8|. Felt pads 85 having curved faces are set up againstthe bottom face of the bar 8I. Strips of abrasive fabric 86 arestretched over the felt pads 85 and are held thereby the spring clips84. The abrasive strips 86 are narrow (in practice less than an inch inwidth), and they are spaced apart so that the intervening space issubstantially over an inch in width. These measurements are not criticaland may be varied as desired. There is clearance between the bar BI andthe surface of the metal sheets heldon the work table, so that only theabrasive surfaces of the pads contact the sheets during rotation of thespindles. The abrasive fabrics 86 carry a fine grit, which may consistof alumina particles or other suitable abrasive material secured to thefabric by suitable adhesive. Several A valve 60 is located in a liquidsupply pipe 6I.

A pipe 62 depends from valve 68 and is telescoped into the top end ofthe hollow transmission shaft 5|, whereby to supply flushing liquid intothe hollow spindle 51.

Lubricators for bearings 53 and 52 are indicated at 60 and SI.

Casing members are fixed on the carriage 32, and each of these members65 has a vertical bore 650. which houses a double end tubular carrier 69having upper and lower ball bearings 66 and 61. The hollow spindle 51runs in those ball different fabrics are used in a complete grinding andpolishing operation on a sheet. The work begins with fabric carrying thecoarsest grit in the range used, and as the work proceeds other fabricscarrying successively finer abrasives are used. In the finishing ofphoto-engraving plates, for example, the coarsest grit may be No. in therecognised trade usage, and the finest may be No. 320 in that usage.Pressure is applied to the grinding heads during rotation of thespindles by reason of the weight of spindle section 51, carrier 69 andthe associated parts, supplemented to the required degree by the tensionof the springs 10. The pressure is varied according to the nature of thesheet metal which is being ground. In the case of zinc, a satisfactorytotal downward pressure on each grinding head is about 15 lbs.

It will be noted that the bar 8I on each grinding head is bored axiallyat 8Ia so as to communicate with the bore of the hollow spindle 51 andto open onto the metal sheet between the abrasive pads on each head. Bymeans of the pump 45, kerosene or other appropriate flushing liquid isforced up into an overhead tank (not shown), and from the tank theliquid fiows in a steady stream at constant pressure down through thepipe BI and thence through shaft 5I, spindle 51 tubular socket 83 andopening 8Ia. of the grinding head to a location on an underlying metalsheet between the abrasive elements on the revolving head.

In practice, as in the grinding and polishing of photo-engraving plates,thegrinding'pads on heads 88 are equipped with abrasive fabrics of thedesired gauge after telescoping carrier 69 and spindle 51 upwardlyagainst the tension of the springs 10. For effecting this movement ofthe spindles, a cam roller 92 is secured to each head piece 13, and acam bar 93, having for each roller stepped surfaces 94 and 95 connectedby an inclined cam surface 96, is mounted for reciprocation back andforth beneath the rollers.

The metal sheets to be finished are placed on the work table I while thepads are raised. The spindles and grinding pads are rotated at highspeeds, for example, about 2200 R. P. M., although higher or lowerspeeds than this may be used. While the pads are raised, the carriage 32and the table ID are started in motion in their crosswise rectilinearpaths at speeds such that the paths traversed by each set of rotatingpads will overlap repeatedly during the course of the operation. Therevolving grinding pads are then lowered to their normal positionsbearing on the sheets, and the continued rotation of the pads andmovement of the table l0 and carriage 32 result in a grinding of thewhole surface of the sheet in overlapping swaths in a manner whichensures .equality and evenness in the surface finish. During all of thisgrinding, a stream of flushing liquid is continuously fed through eachspindle and is flooded onto the surface of the sheet from a point insidethe circular path of the pads. The heavy flush of liquid thus floodedonto the sheet surface, aided by centrifugal force imparted by the rapidrotation of the grinding pads, sweeps away free metal immediately as itis rubbed off the sheet surface. The liquid, together with the particlesof metal, flows into the gutter l4, and thence to the clarifier chamber48. Pump 45 returns the clarified liquid to the same cycle of operation.

When a grinding operation has been completed, the pads should be raisedfrom the sheet before their rotation-or the movement of the table orcarriage is stopped.

The flushing liquid fed through each spindle is thrown into the path ofthe pads, where it is overrun by the rapidly revolving abrasive. Metalparticles removed by the abrasive are held in liquid under the pad, andthe spinning of the pad causes this liquid and the free metal to bethrown outwardly and away from the grinding swath. When the padsapproach a portion of the sheet on which used liquid and free metal mayhave collected, the continuous outward sweep of liquid from the swath ofthe pads brushes away this used liquid and free metal and clears thesheet surface, so that danger of overtaking and overrunning metalparticles that have already been removed is avoided.

Thus, the described method and apparatus are exceedingly effective formaintaining a clear surface on the metal sheet throughout the grindingoperation. Clogging of the abrasive fabric with metal dust is avoided,and scratching of the plate surface is consequently obviated. Thegrinding time is shortened, and a uniform smooth finish is obtained onthe-sheet surface.

It'is important that the grinding pads shall not be subject tomechanical disturbance by the driving equipment. Such disturbance isavoided since the spindle 51, the parts which are carried by it and thecarrier 69 in which it is housed are not constrained in lateraldirection by belt pull on the pulley 55, and the spindle 51 is free torotate steadily on its own gyrostatic center,

unaffected by the drive coupling through the ly, the respective machinesbeingv armed with abrasive fabrics of appropriate gauge. The number ofto and fro movements of the machine table and the number of traversemovements of the spindle assembly will necessarily vary according to thenature of the metal of which the sheet is composed and the type ofsurface finish desired to be attained.

In the grinding or polishing of engravers sheets, which should have auniform thickness and uniform surface finish over their entire surface,the path of movement of the table I0- and the carriage 32 should becoordinated so that the circular swath of the grinding pads will extendsomewhat beyond the edges of the sheet but not to a point where theweight of the spindle assembly would not be borne entirely by the sheet.

It will be understood that a grinding fabric or paper coated'with fineabrasive tends to clog or load up with metal more easily than in thecase of coarse abrasive, because there is less free space for movementof liquid and metal particles. For a constant rate of flow of keroseneor other flushing liquid onto the sheet, the Width of abrasive materialin contact with the sheet, in the direction of movement of the pad, ispreferably less in the case of a fine abrasive than when using coarseabrasive. In thisway the effective flushing action of the liquid isincreased to compensate for the greater difficulty in flushing away thefree metal.

In the finishing of accurately planed zinc sheets, such as producedaccording to the disclosure of my copending application, filed March 29,1937, now United States Patent No. 2,216,538 to meetthe requirements ofhigh grade photoengraving work, it is found in practice that about tenminutes grinding is effective for a complete grinding and polishingoperation on a sheet measuring 20 x 40 inches. The grinding pads operatewith clean surfaces because of the immediate clearance of the removedmetal from their path, so that in practice comparatively large amountsof metal may be removed from each sheet per minute in the grindingoperation, without diminishing the accuracy of the planed surface of thesheet.

It will be understood that many details of construction and operationwhich have been described in reference to the illustrated embodiment ofthe apparatus are set forth merely for clarity of disclosure, and thatnumerous variations and modifications may be made without departing fromthe contributions of the invention, as intended to be set forth in theappended claims.

I claim:

1. The method of producing a uniform smooth surface finish on a metalsheet which comprises rotating a yieldable pad surfaced with abrasivefabric on a surface of thesheet at high speed about an axis constantlyat right angles to the sheet, while effecting relative movement betweenthe sheet and said axis whereby to traverse the rotating pad inoverlapping swaths uniformly covering the entire area of said surface.yieldably holding the abrasive surface of the rotating pad underconstant pressure against said sheet surface during said movement, andsimultaneously flooding a constant stream of gritfree flushing oil ontothe said surface from a point adjacent said axis of rotation.

2. The method of producing a uniform smooth surface finish on a metalsheet which comprises" starting rotation of a yielding pad surfaced withabrasive at high speed about an axis at right angles to the sheet,starting relative movement between the sheet and said axis such as totraverse the rotating pad in overlapping swaths uniformly covering anentire surface of the sheet, thereafter applying the rotating padagainst said surface, pressing the abrasive surface of said rotating paduniformly against said sheet surface during said relative movementbetween the sheet and said axis, and throughout the grindingoperationafiooding a constant stream of grit-free flushing oil onto saidsheet surface from a point adjacent said axis of rotation to cause theabrasive to overrun av film of the oil and the oil to hold and flushaway freemetal immediately after the same has been abraded from thesheet.

3. Apparatus for grinding or polishing the sur faces of metal sheetscomprising continuously operating means for reciprocating a sheet in onelinear path, means for repeatedly traversing abrasive pads over asurface of the sheet in a crosswise linear path and means for rotatingsaid pads at high speed in a plane parallel to the sheet, saidlast-recited means including a,

tubular vertical spindle having a pad-holding head fastened to its lowerend, said head having an axial bore communicating with said spindle, atubular transmission shaft fixed against vertical movement andtelescoping into said spindle, means mounting said spindle to permitvertical movement of the same while rotating, cooperating means securedto said transmission shaft and said spindle for transmitting rotation tosaid spindle without restraining it freedom xto move vertically, andmeans for supplying a and means for supplying liquid into said spindle;

for delivery to a point between said pads during rotation thereof.

5. In an apparatus for grinding or polishing the surfaces of metalsheets, a vertical hollow spindle. a transverse block secured to thelower end of the spindle and having an opening there throughcommunicating with the spindle, spaced yieldable pads fixed to thebottom of said block on opposite sides of said opening, means on saidblock for fixing an abrasive fabric over each v of said pads. meansincluding a hollow transmission shaft telescoped into said spindle forrotating said spindle, block and pads, means for supplying liquid intosaid shaft to flow through grinding head having abrasive-surfacedyieldable grinding pad secured to the lower end of said spindle andadapted tobear upon the surface of a sheet on said table, continuouslyoperating means for reciprocating said table in a linear path beneathsaid spindle,,continuously operating means for reciprocating saidcross-head and spindle in a cross-wise linear path above said table,means for rotating said spindle and head athigh speed While said tableand cross-head are in motion, and means for raising or lowering saidhead with respect to said table while the spindle is rotating.

7. Apparatu for grinding or polishing the surfaces of metal sheetscomprising a sheet-holding table, a cross-head mounted above said table,a plurality of hollow vertical spindles secured to said cross-head, agrinding head having abrasivesurfaced yieldable grinding pads secured tothe lower end of each spindle and adapted to bear upon the surface of asheet on said table, continuously operating means for reciprocating saidtable in a linear path beneath said spindles, continuously operatingmeans for reciprocating said cross-head and spindles in a cross-wiselinear path above said table, means for rotating said spindles and headsat high speed while said table and cross-head are in motion, means forfeeding a continuous stream of flushing liquid through each hollowpindle and onto a sheet inside the path of rotation of the pads whilethe spindles and heads are rotating, and means for simultaneouslyraising or lowering said heads with respect to said table while thespindle are rotating.

8. In an apparatus for grinding metal surfaces, a rotary spindle havingabrading means fastened to its lower end, a non-rotary carrier sleevesurrounding said spindle and having bearings on its upper and lower endsholding said spindle in a fixed and coaxial relation thereto, meansmounting said carrier for free ,sliding movement in axial direction,said means including a housing fixed against axial movement, and springmeans connected with said carrier and said housing for pressing thecarrier and said spindle downwardly in axial direction and therebyyieldably holding said abrading means under constant pressure against asurface to be ground.

9. In an apparatus for grinding metal surfaces, a vertical hollowspindle having abrading means fastened to its lower end, a non-rotarycarrier holding said spindle in a fixed coaxial relation thereto, meansmounting said carrier for floating movement in axial direction, saidmeans including a fixed housing supporting said carrier for verticalsliding movement relative thereto and springmeans connected with saidcarrier and said housing for pressing the carrier slidably toward asurface to be ground, a hollow transmission shaft telescoped inside theupper end of said spindle, cooperating means connected to said shaft andsaid spindle for rotating the spindle, respectively, with the shaftwhile permitting vertical movement of the spindle, and means for drivingsaid transmission shaft at high speed.

10. Apparatus for grinding metal sheets comprising a horizontal worktable, a vertical spindle mounted above said table, said spindle havingabrading means fastened to its lower end and adapted to bear on thesurface of a sheet on said table, means for rotating said spindle athigh speed, continuously operating means for reciprocating said table ina linear path beneath said spindle and continuously operating means forreciprocating said spindle in a crosswise linear path above said table,said means for reciprocating said table being operative to move saidtable at a constant rate intermediate the extremities of its path ofmovement and including means for delaying appreciably the restarting ofthe table movement at each end of said path whereby to obtain uniformabrasion of the entire surface.

11. Apparatus for grinding metal sheets comprising a horizontal worktable, a vertical spindle mounted above said table, said spindle havingabrading means fastened to its lower end and adapted to bear on thesurface of a sheet on said table, means for rotating said spindle athigh speed, continuously operating means for reciprocating said table ina linear path beneath said spindle and continuously operating means forreciprocating said spindle in a crosswise linear path above said table,said means for reciprocating said table and spindle each being operativeto move the respective table or spindle at a constant rate oversubstantially all of its linear path of movement, but each includingmeans for delaying appreciably the restarting of the respective table orspindle movement at each end of its path.

12. The method of grinding or polishing the surfacesof metal sheets soas to produce thereon a uniformly smooth surface finish which comprisesrotating spaced yieldable pads surfaced with abrasive fabrics at highspeed in an annular path about a common axis at right angles to thesheet surface, simultaneously moving the sheet to and fro in a fixedlinear path beneath said pads, simultaneously moving said pads bodily toand fro over the sheet in a fixed linear path transverse to the path ofthe sheet, yieldably holding the abrasive surfaces of said rotating padsunder constant pressure against said sheet surface during the aforesaidsimultaneous movements whereby to abrade the sheet surface uniformly byoverlapping circular swaths of said pads, and simultaneously flooding aconstant stream of grit-free oil onto said sheet surface from a pointinside the path of rotation of said pads so as to keep the abrasiveworking through films of oil and continuously to flush oil and any freemetal particles away from the abrasive.

13. The method of grinding or polishing the surface of a metal sheetwhich comprises rotating a grinding pad surfaced with abrasive at highspeed in progressively overlapping annula swaths on said surface,simultaneously flooding a stream of grit-free flushing oil onto thesurface and across said paths from a point inside of said paths to keepthe abrasive working through oil and flush away free metal immediatelyafter the same has been abraded from the sheet, collecting used flushingoil flowing from the sheet and treating the same to separate free metaltherefrom, recirculating and reusing the treated grit-free oil asaforesaid, and recovering the separated free metal.

14. The method of grinding or polishing the surface of a non-ferrousmetal sheet which comprises rotating a yieldable pad surfaced withabrasive fabric at a high speed in progressively overlapping annularswaths on said surface and continuously flowing across the path of saidpad a stream of mobile, non-corrosive oil containing yieldable padhaving a surface composed of abrasive alumina particles and continuouslyflowing across the'path of said pad a stream of mobile, non-corrosiveoil containing kerosene oil.

16. The method of grinding or polishing the surface of a zinc sheetwhich comprises rotating a yieldable pad surfaced with abrasive fabricat a high speed on said surface and simultaneously flowing across thepath of said pad a stream of kerosene oil.

1'7. The method of grinding or polishing the surface of a copper sheetwhich comprises rotating a yieldable pad surfaced with abrasive fabricat a highspeed on said surface and simultaneously flowing across thepath of said pad a stream of mobile, non-corrosive oil includingstearine oil.

18. In an apparatus for grinding or polishing metal sheets, a verticalhollow spindle having a grinding block fastened to its lower end,diametrically opposed, abrasive-covered pads secured to the underside ofsaid block, a passage extending through said block from said hollowspindle and opening at a point between said pads, a non-rotary carrierholding said spindle in vertical position, means mounting said carrierfor free sliding movement in axial direction, a hollow transmissionshaft telescoped inside the upper end of said spindle, cooperating meansconnected to said shaft and said spindle, respectively, for rotating thespindle with the shaft while permitting free vertical movement of thespindle, tension spring means connected with said carrier and saidmountin means for yieldably holding said pads against a work sheet underconstant pressure, means for driving said transmission shaft at highspeed, and means for introducing flushing liquid into said transmissionshaft.

19. The method of producing a uniform smooth surface finish on metalwork which comprises rotating a yieldable pad covered with abrasivefabric in progressively ,overlapping annular swaths on a surface of thework so as substantially uniformly to abrade the entire surface, whileflowing a stream of grit-free film-forming liquid on to said surfacefrom a point inside of said swaths and yieldably pressing said padagainst said surface with a force suflicient for the abrasive to workthrough the resulting liquid film and abrade said surface, therebymaintaining protective liquid between the pad and said surface andcausing liquid and any free metal particles constantly to be swept awayfrom said pad.

20. The method of producing a. uniform smooth surface finish on a metalsheet which comprises holding thereagalnst a yieldable pad covered withabrasive paper and rotating said pad bodily in an annular path about anaxis perpendicular to the sheet while traversing the rotating padprogressively and substantially uniformly over the entire sheet surface,and simultaneously flowing a stream of grit-free oil on to the surfaceand across said path from a point inside of said path so as to maintaina film of oil between said pad and the surface and cause oil and anyfree metal particles constantly to be swept away from said pad.

21. The method of producing a uniform smooth surface finish on a planemetal surface which comprises rotating thereon a yieldable pad facedwith adherent abrasive at high speed and in progressively overlappingannular swaths traversing the entire surface, while flowing a stream ofgritfree oil on to said surface from a pofmt inside of Saidswaths,thereby causing the abrasive conaseasos tinuously to work through theoil fllm'and centriiugally expelling oil and any free metal particlesaway from the abrasive.

22. The method of producing a uniform smooth surface finish on metalengraving sheets which comprises holding against a surface of each sheeta plurality of spaced yieldable pads covered with abrasive fabric androtating said pads bodily in a common annular path about an axisperpendicular to the sheet while traversing the rotating padsprogressively and substantially uniformly over the entire sheet surface,and simultaneously flowing a stream of grit-free oil on to the sheet andacross said path from a point inside of said path so as to keep theabrasive working through the oil and constantly to sweep oil and anyfree metal particles away from the abrasive.

23. In an apparatus for grinding metal sheets. a rotary spindle havingabrading means fastened to its lower end, a non-rotary carrier sleevesurrounding said spindle and having ball bearings at its upper and lowerends holding said spindle in a fixed and coaxial relation thereto, afixed housing surrounding said carrier intermediate the end portionsthereof, cooperating means on said carrier and said housing to permitfree axial movement but prevent rotation of said carrier, spring meansconnected with said carrier and said housing for yieldably pressing thecarrier and spindle axially toward a surface to be ground and flexibledust collars extending between the end portions of said sleeve and therespective end portions of said housing.

THOMAS JEROME MASSE.

CERTIFICATE OF CORRECTION. Patent No. 2,560,5oh. October 17, 19%.

moms JEROME MASSE.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 5,first column, line 5, claim 2, for the word "yielding" read-yieldable--; and second column, line 614., claim 9, strike outrespectively," and insert the same after "spindle" in line 65, sameclaim; and that the said Letters Patent should be read with thiscorrection therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 16th day of January, A. D. 19LL5.

Leslie Frazer Acting Commissioner of Patents.

